The studies here proposed are intended to determine the quantitative changes with age in selected parameters of proliferative activity, structural organization and metabolic activity in palatal and buccal mucosa of rats 6 and 30 months old. Rats reared under conditions eliminating as much as possible the cumulative effects of environmental insults will be studied in order to enable us to distinguish between those inevitable changes which have occurred as the result of aging per se and those resulting from disease of environmental origin. Appropriate methods of biometrics, light and electron microscopic histology, biochemistry and stereology will be applied. The effects of aging will be studied in parameters selected to determine (1) for proliferative activity: the rate of cell division, synthesis time and growth fraction, and turnover and transit times in differentiating and keratinized compartments; (2) for structural organization: the dimensions and dry weights of epithelial compartments and their cells and the ultrastructural characteristics of the chief products of synthesis, membrane-coating and keratohyaline granules and tonofilaments; (3) for metabolic activity associated with proliferation and keratinization: the rates of glucose and fatty acid utilization, the solubility of proteins and the activities of two marker enzymes for keratinizing processes; (4) for the supporting tissues: capillary supply and the relative volumes of collagenous and elastic fibers. The same parameters will be studied in young and old rats kept for a five week period on an isocaloric liquified diet and a solid diet restricted to 60 percent of the ad lib. food intake. The differential effects of these diets in young and old animals will depend on, and therefore reveal, the possible deleterious influence of age changes on the capacities of the two regions to tolerate dietary alterations - of a kind frequently adopted as changes in food habits by the aging human.